Conventional motor control for electric drive systems utilizes two-dimensional look-up tables to generate maximum torque limits (e.g., for both motoring and regenerating operations). Generally, maximum torque limits are required to accomplish various performance requirements of a drive system. For example, maximum torque limits are typically required for maintaining the vehicle battery within a predetermined range of operating voltage and power. One method of maintaining the battery within the predetermined operating range is to limit torque in the traction system. For example, during motoring, a motoring torque may be limited to keep the battery voltage above the minimum operating voltage. In another example, during regeneration, a regenerating torque may be limited to keep the battery voltage below a maximum value. In other cases, the torque limits may reflect the maximum torque capability of the motor to operate within specified voltage and current limits of the drive system under existing operating conditions.
Reference to torque limit look-up tables may be used when generating torque commands. Typically, the maximum torque limits generated from the look-up tables are calculated at a steady state stator temperature. However, during vehicle operation, the temperature of the drive system may vary. As a result, the maximum motoring and regenerating torque that the drive system can produce may differ (e.g., as a function of temperature) from the maximum torque limits generated from the look-up tables.
Accordingly, it is desirable to provide methods and systems for adjusting torque commands of permanent magnet machines that compensate for magnet temperature variation. Additionally, it is desirable to provide methods and systems for determining torque limits of permanent magnet machines that compensate for magnet temperature variations. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.